It has been known for some years to determine the content of molecular oxygen in a sample by using optical methods based on luminescence quenching. In general, these methods comprise measuring the luminescence intensity and/or the luminescence lifetime of a suitable luminophor, the luminophor being in contact with an oxygen-containing sample and being exposed to illumination. The basic feature of luminescence quenching is the deactivation of the luminescing excited electronic state of the luminophor taking place on collision with oxygen molecules. As the average number of luminophor molecules in the excited electronic state is reduced by the interaction with the oxygen molecules, the luminescence intensity and the excited state lifetime of the luminophor are reduced. The magnitude of the reduction is connected with the number of oxygen molecules in contact with the luminophor through the Stern-Volmer equation EQU M.degree./M-1+K.sub.sv .multidot.[O.sub.2 ]
see e.g. IUPAC Commission on Photochemistry, and "Glossary of Terms used in Photochemistry, part III", EPA Newsletter, July 1986. M.degree. and M of the above equation designate the luminescence intensity or the excited state lifetime of the luminophor in the absence and presence of oxygen, respectively. [O.sub.2 ] designates the concentrations of molecular oxygen corresponding to the M-value measured. K.sub.sv is the so-called Stern-Volmer constant explained in the above reference. By using this equation and correlating it to samples of known oxygen content, it is possible to determine the oxygen content of a sample. Photometric determination of the oxygen content in blood or other media b.sub.V the so-called luminescence quenching is known from i.a.:
Bacon, J. R and Demas, J. N., "Determination of oxygen concentrations by luminescence quenching of a polymer immobilized transition-metal complex", Anal. Chem., 59, 1987, 2780-2785,
Longmuir, I. S. and Knopp, J. A., "Measurement of tissue oxygen with a fluorescent probe", Journal of Applied Physiology, 41, 1976, 598-602,
Waughan, W. M. and Weber, G., "Oxygen quenching of pyrenebutyric acid fluorescence in water. A dynamic probe of the microenvironment", Biochemistry, 9(3), 1970, 464-473,
Bergman, I., Nature 218, 1958, 376,
Stevens in the specification of U.S. Pat. No. 3,612,866,
Stanley in the specification of U.S. Pat. No. 3,725,658,
Bacon, J. R. and Demas, J. N. in the specification of
British patent application GB 2132348,
Peterson et al. in the specification of U.S. Pat. No. 4,476,870,
Buckles, R. G. in the specification of U.S. Pat. No. 4,399,099,
Hirschfeld, T. in the specification of U.S. Pat. No. 4,542,987,
Dukes et al., in the specification of U.S. Pat. No. 4,716,363,
Lubbers et al. in the specification of U.S. Reissue Pat. No. 31,879,
Kahil et al. in the specification of International patent application WO 87/0023,
Murray, R. C., Jr. and Lefkowitz, S. M. in the specification of European patent application EP 190829,
Murray, R. C., Jr. and Lefkowitz, S. M. in the specification of European patent application EP 190830, and
Hesse, H. C. in the specification of East German patent DD 106086.
Determination of the intraarterial values of the blood gas parameters pH, oxygen (O.sub.2) and carbon dioxide (CO.sub.2) by means of a fluorescence based measuring system is known from Miller et al,. "Performance of an in-vivo, continuous blood-gas monitor with disposable probe", Clin. Chem. 33(9), 1987, 1538-1542.
Extracorporeal determination of all three parameters by means of another fluorescence based measuring system Gas-STAT.TM., produced by Cardiovascular Devices Inc., USA, is finally described i.a. in brochures concerning this system and in the article by Clark, C. L., "Early clinical experience with Gas-STAT", J. Extracorporeal Technol., 18(3), 1986, 185-189. The determination of the blood gas parameters proceeds continuously in the GAS-STAT.TM. system. Inside a cuvette, which is inserted in the extracorporeal circulation established at a cardiac operation, fluorescence based sensors are placed. Via optical fibers excitation radiation is provided and emitted fluorescence radiation is taken away. The intensity of the latter depends of the concentration on the matter measured by the relevant sensor.
None of these publications relating to photometric analysis of oxygen describes an in vitro method for determination of oxygen in discrete samples and based on simple sample handling principles.
In vitro determination of oxygen in a blood sample has so far mostly been performed by means of blood gas analyzers as, e.g. the blood gas analyzers produced and sold by Radiometer A/S, Copenhagen, under the name ABL Acid-Base Laboratory.
These analyzers are mechanically complex, since the blood samples i.a. have to pass through the very fine fluid conduits of the analyzer, in which conduits electrochemical sensors are built-in. Blockage in the conduits or coatings on the active surfaces of the sensors can easily occur and interfere in or destroy a measurement.
On account of these circumstances the existing equipment requires frequent maintainance performed by specially trained personnel, and the equipment will normally be placed in a laboratory situated at a certain distance from the patient. A response period of more than 10 min. and normally up to half an hour from the time of the sampling to the moment of obtaining the analytical result is therefore not unusual. Beyond that the waiting period can be unfortunate in connection with the medical treatment of the patient, the relatively long waiting period also has the consequence that the sample is to be kept cooled down to app. 0.degree. C. This is due to the fact that at higher temperatures the metabolic processes of the blood will cause changes in the blood gas parameters during the relevant periods.
Another disadvantage of the existing equipment is that there exists a certain risk for the operator to get in touch with sample residues with the health risks this may imply in the form of transfer of infections, etc.
British patent application GB 2 025 065 (Meiattini, F. et. al.) a mechanically simpler in vitro system comprising a plunger syringe for withdrawal of a blood sample. The blood sample is analysed by means of sensors incorporated in the syringe plunger is thereby avoiding transfer of the sample to a separate measuring chamber.
The sensors are adapted for connection with an analyzer via conductors for registering, processing, and printing out analytical data. The specific sensors described in the specification of the said British patent application GB 2 025 065 are electrochemical sensors for blood gases and blood electrolytes.
It shall finally be mentioned that the technological basis also comprises other clinical chemistry analyzers consisting of a combination of disposable components, which are only used for one single analysis operation and only get in touch with one single sample, and an analyzing section adapted for receiving the sample-containing, disposable device and containing the additional components necessary for accomplishing a clinical chemical analysis. Special blood gas analyzers are, however, not known among these. Apart from analyzers of the type disclosed in the abovementioned GB 2025065 wherein the sensors are electrochemical sensors, there are no known in vitro oxygen analysers based on disposable components.